>>719243384
Because the previous Kirby game before FL brought dam near everyone back already in the minds of the general fanbase (2018 was 7 years ago).
https://wikirby.com/wiki/Kirby_Star_Allies#Dream_Friends
Given that the Susie model in Riders looks to be a touched up one from SA, I can see HAL doing the same thing for the characters here.
Meanwhile popular Mario characters like Diddy and Petey are no shows in the big dam new game for a new system, and other popular characters from older titles (many who might never be seen again unless that particular game is remade) get nothing.